Through the years, a variety of techniques have been developed for delivering nutrients to growing plants and for extending or delaying the release of nutrients from a fertilizer.
In one approach, a granular or particulate fertilizer is formed which gradually releases its components to the environment. The rate of release of nutrients from the fertilizer particles is influenced by the composition of the particulate fertilizer, often by the way the fertilizer composition has been granulated or by nature of the binder used to assist granulation of the fertilizer.
In another approach, a slow or delayed release coating is applied over the granular fertilizer. Such coatings have included sulfur, waxes and resins. U.S. Pat. No. 4,019,890, for example, describes completely coating a granular fertilizer using a solution of a highly water resistant resin. The patent teaches the use of a solution of a thermoplastic resin, such as a polyolefin, in a hydrocarbon or chlorinated hydrocarbon solvent, which is rapidly dried upon spaying onto the fertilizer granules. U.S. Pat. No. 4,881,963 also describes a coating for a granular fertilizer, the coating comprising an ethylene-carbon monoxide copolymer and optionally one resin selected from either a rubbery resin, such as natural rubber, polyisoprene or SBR, or an ethylene-vinyl acetate copolymer.
Related technologies also are described in AU 704,560, JP 9249478 and JP 9309783.
In these approaches, the coating itself generally has little to no nutrient value and functions solely to regulate the release of nutrients from the encapsulated granular fertilizer.
Nitrogen fertilizer is often applied as a formulated (N—P—K) solid, granular or powder, or sometimes as a liquid to an area to be fertilized. The solid form is generally fast release, but it can be made slow release by various coatings (as described above). Alternatively, a reduction in nitrogen availability also can be obtained by using enzyme inhibitors. The liquid form may include both fast-acting and slow release forms of nitrogen. Some of the recognized disadvantages of such nitrogen fertilization involve run-off into rivers and streams, ammonia emissions and nitrate leaching.
The prior art does not describe how to introduce a particulate source of slow release nitrogen using a coating on a solid support, or on an aggregate material, as a way to deliver the nitrogen over a prolonged period of time for enhancing plant development and growth and for minimizing the problems of run-off and ammonia emission associated with many of the common forms of nitrogen fertilization. The present invention proposes to supply a particulate slow-release nitrogen fertilizer as a coating on a solid substrate or on an aggregate material.